Lawful interception is the lawfully authorized interception and monitoring of communications of an intercept subject. This is the process of intercepting within a network, communications between parties of interest. The interception is legally authorised and is conducted without the intercepted parties being aware of it. Lawful Interception is often referred to as ‘wiretapping’ or ‘phone-tapping’.
Several techniques where introduced to allow lawful interception in telephone networks, but solutions based on line-switched networks are not applicable in packet switched networks like voice over IP.
EP 1 389 862 discloses a lawful interception device to monitor media streams of two IP parties includes a SIP (Session Initiation Protocol) proxy server or a MGC (Media Gateway Controller) to detect information in the signalling information being transmitted between the two IP (Internet Protocol) parties and to generate instructions out of the detected signalling information for instructing a RTP (Real-time Transport Protocol) proxy server to create channels to bypass a media stream to be intercepted via an intermediate storage medium. Due to adaptation of connection parameters in the SDP (Session Description Protocol) part of the SIP messages sent to the IP parties the interception is transparent to the IP parties.
Lawful interception in state of the art networks need especially designed proxy servers.